Solder flux formulations typically consist of a fluxing component or agent dispersed or dissolved in an aqueous or organic solvent. These fluxes are generally applied to surfaces or locations required to be soldered together. The application of the flux is performed in any number of ways, such as coating, dispensing, dipping, spraying, or otherwise selectively or globally depositing the flux on the surfaces to be soldered together. In the electronics industry, for example, electronic components are soldered to printed circuit boards. A solderable material, typically a tin-lead alloy, is applied either to the component, the circuit board, or both, along with the flux, and the assembly is heated and the flux activates the surfaces of the metals. When the solder melts, it alloys with both the electronic component and the printed circuit board, to form an electrical and mechanical joint between the component and the circuit board.
For most uses in the electronics industry, it is desirable to use a flux composition which is non-corrosive and non-conducting. For this reason, rosin based flux compositions are widely used in the commercially available fluxes made specifically for manufacturing surface mounted electronic assemblies. If more reactive fluxing compositions are used, they typically leave residues which are corrosive and/or conductive. However, higher reactivity is, in some ways, desirable, in that it aids in removing oxides which may form on the metal surfaces to be soldered, thereby providing a strong solder bond. However, the use of such fluxes also has a number of disadvantages. Because the residues from rosin based fluxes tend to be sticky, they interfere with automatic testing of the circuit, and unsightly, attract dirt and moisture from the environment, they prevent effective encapsulation or conformal coating of the circuitry, and are hygroscopic.
Because of these disadvantages, flux residues are typically removed in a post-solder cleaning operation. A common procedure is to use an aqueous or organic solvent to remove the flux residues. Water is preferred because it does not leave an objectionable residue. However, water is typically an ineffective agent since many of the residues, such as the rosin, are only slightly soluble in water. Organic solvents are more effective but are less desirable because they are expensive to purchase initially, and are also expensive and difficult to dispose of. One class of organic solvents that has historically obtained widespread use is the chlorofluorocarbons (CFCs) because they are inert and volatilize after cleaning. CFCs have recently come under strong attack because of their tendency to deplete the ozone layer. With severe restrictions placed on the manufacture and use of CFCs, it is clear that this method of cleaning will be totally unsuitable in the near future.
For these and other reasons, the prior fluxing compositions are not preferred, and it would be advantageous to discover a new fluxing composition that would avoid one or more of these disadvantages.